Helicopter-borne Measurements

Flight over the measurement region

Helicopter-borne measurements of radioactive materials (aero-gamma spectrometry) provide substantial advantages over other measuring techniques in an emergency, such as an accident in a nuclear power station. Depositions of radioactive materials in the soil can be assessed promptly, flexibly and selectively, as well as on a large scale without having to enter highly contaminated areas.

These measurements permit to detect and quantify artificial or naturally occurring radioactive materials in, or on, the soil or in the air, as well as potential radioactive sources indoors.

Objectives of measurement exercises

Helicopter-borne measurements are very challenging. Therefore, regular measurement exercises are performed in order to practice and steadily improve the cooperation between the German Federal Police (BPOL) and the scientific and technical staff of the BfS. The exercises are also aimed at optimising the measurement and evaluation procedures developed at the BfS.

In addition, the BfS and BPOL organised international measurement campaigns and participated in measurement exercises in Finland, Scotland, Sweden, France and Switzerland.

Measuring systems operational at any time

Four airworthy measuring systems operational at any time are available at the BfS Munich and Berlin locations. In the event of an emergency, these are a valuable supplement to the 1,800 stationary probes operated by the BfS, which continuously measure the ambient dose rate (ODL) and forward the data to a central system – the "Integrated Measuring and Information System" (IMIS).

Annual measurement exercises

To ensure immediate operational readiness of the aero-gamma spectrometry system in the event of an emergency, exercises are carried out annually in several Federal States of Germany or neighbouring countries. For the measurement flights, type EC 135 helicopters of the German Federal Police or of civil protection services are equipped with special devices for the detection of gamma emitting radionuclides.

Together with the measured data, the geographic coordinates and the flight altitude are recorded in order to plot the spatial distribution of the detected radioactive materials after each measurement flight.

How does the measurement exercise take place?

The Federal Police carry out the measurement flights and is responsible for the exact positioning of the helicopters in the areas to be mapped. The BfS staff ensure the functionality of the measurement technology, record the measured data and evaluate the data immediately after the measurement flights. As a rule, BfS staff members always accompany pilots and aircraft technicians of the Federal Police on measurement flights.

During a measuring flight, the BfS staff member in the helicopter (operator) is able to check the parameters of the detectors at any time. Selected information is displayed on the screen. This enables the operator to recognise radiological abnormalities already during the measurement flight and highlight the data set accordingly. The program automatically records the measured values of these highlighted items.

First review and evaluation of the measurement data

Immediately after the landing, the recorded data sets are copied on an evaluation computer, which is situated either in an evaluation room or in a car next to the landing place. Subsequently, a first review and evaluation of the measurement data is performed, e.g. by plotting the computed values of ambient dose rate against the geographic coordinates and a map. Thus, it is possible to promptly recognise suspicious values and forward the data to the competent authorities. In addition, the further flight planning can be immediately adapted to the radiological situation.

Is there a hazard for the crew and measurement team during an operation?

During a measurement flight, the ambient dose rate in the helicopter is measured and the accumulated dose recorded. If the ambient dose rate exceeds a value of 25 mSv per hour, the operation is stopped to determine alternative strategies.

Reducing radiation exposure

The radiation exposure of the staff can be reduced as follows:

• Not directly overflying potentially contaminated areas,
• Selecting a higher flight altitude,
• Applying special flight procedures,
• Keeping more distance when approaching radiologically suspicious areas.

Strategic orientation of air-borne and car-borne measurements

Before measurement cars are deployed in an investigation area, the spatial distribution of radioactive materials is mapped using helicopter-borne measurement systems. If the evaluation identifies areas with ambient dose rate values clearly exceeding the natural radiation background, detailed radiological investigations using car-borne measurements can be performed in these areas.

For this purpose, particularly equipped cars are available at six locations in Germany, used for regular measurements for quality assurance of the measured ambient dose rate.

In order to assess the actual values of specific activity, these investigations can be supplemented by

• Performing on site measurements, and
• Taking soil and plant samples with subsequent radiochemical laboratory analysis.